Abstract

The present study examined the tissue distribution of rat sulfotransferase (SULT) mRNAs to assess the relative contribution of each tissue to the process of sulfation. The SULT isoforms examined were male-dominant SULTs (SULT1A1, SULT1C1, and SULT1E2), female-dominant SULTs (SULT20/21, SULT40/41, and SULT60), and the recently cloned, non sex-dependent SULT (SULT1B1). SULTs fall into two distinct classes based on substrate preference: phenol SULTs (SULT1A1, SULT1B1, SULT1C1, and SULT1E2) and hydroxysteroid SULTs (SULT20/21, SULT40/41, and SULT60). The following tissues were analyzed for SULT mRNA expression: liver, brain, lung, heart, intestine, kidney, adrenal, prostate, testes, ovary, uterus, and spleen by Northern blot analysis with [α-³²P]dATP-labeled oligonucleotide probes specific for individual SULT mRNAs. Tissue expression levels of each SULT were quantified and compared with liver expression by phosphor-autoradiographic analysis. Male-dominant SULT expression was observed in many organs, where SULT1A1 was expressed in liver, brain, lung, heart, intestine, kidney, adrenal, testes, and spleen; SULT1C1 expression was observed in liver, kidney, and spleen; and SULT1E2 expression was observed only in liver and heart. The female-dominant SULTs exhibited a more limited tissue distribution. Expression of SULT20/21 and SULT60 was observed only in liver and adrenal gland, whereas SULT40/41 expression was observed only in liver. SULT1B1 was expressed to a similar extent in tissues of male and female rats and was detected in liver, intestine, and kidney. Expression of SULT mRNAs in liver was much higher than in other tissues, except for SULT1A1, which exhibited substantial expression in lung, and SULT1B1, which was expressed at relatively high levels in intestine. These studies indicate that liver is the most diverse organ with respect to expression of multiple SULT enzymes and is therefore the most significant organ involved in sulfation. In contrast to liver, extrahepatic tissues express specific SULT mRNAs, and this may be important for the physiological role of each tissue.